The industrial production of aluminum requires alumina (Al2O3) to be dissolved in molten cryolite (Na3AlF6) during the electrolysis. The electrolysis is performed by providing a direct current to the alumina and molten cryolite mix via a carbonaceous anode (typically very large—can exceed 1000 kg—and made from petroleum coke and coal tar pitch) and a graphite cathode. The aluminium smelters consume the carbonaceous anodes and this requires their replacement after 20-25 days.
Using anodes of good quality is important not only to provide a stable operation during the electrolysis process, but also to lower the electrical costs. Indeed, defects present in the structure of the anode can lead to the generation of undesirable heat which translates into a loss in energy efficiency (increased electrical energy consumption). Since the direct current involved in such smelters can currently reach up to 600 kA through the anode, reducing the loss in electrical energy consumption can be highly rewarding. Moreover, important fissures can lead to the loss of a relatively large portion of the anode at the bottom of the smelter, which can have a significant impact on plant productivity. Overall, the amount of anodes consumed also has an impact on the amount of greenhouse gases produced.
It was known to measure an average resistivity of a baked anode in conditions simulating the operation condition in order to obtain an indication of anode quality. The anode could be discarded if considered of unsatisfactory quality, in order to address the afore mentioned issues stemming from low quality anodes. Although the existing techniques are satisfactory to a certain degree, there remains room for improvement.